Solar Thermal Collectors area in EnergyPlus

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The answer in this post about solar collectors mentions that you can assign collectors to building surfaces like roofs OR shading surfaces. This is also supported in the Input Output Reference document for EnergyPlus, specifically the description of the Surface Name input field of the SolarCollector:FlatPlate:Water object.

In your case, it sounds like adding 35 shading surfaces each with an area of 2 m^2 above the roof is your best option. Each of those shading surfaces would then be assigned to a flat plate solar collector (35 total of those as well).

Perhaps I am misunderstanding your question, but if you have 35 individual collectors in a single solar thermal system, you could just use a single SolarCollector:* object to represent the entire system. You don't need to use multiple SolarCollector:* objects. And then you could reference a single shading surface.